Blast furnace coke has been used as a reducing agent, a heat source, and a support to maintain gas permeability in a blast furnace. In recent years, there has been a trend toward the production of high-strength coke in order to achieve stable operation at a low reducing agent ratio. Upon producing blast furnace coke, a coal blend in which a plurality of coal brands (2 or more and 20 or less) are blended is commonly used. Thus, methods for predicting the strength of coke produced from the coal blend serving as a raw material has hitherto been studied. For example, the following methods described in items (i) to (iii) are known.
(i) Method for Predicting Strength of Coke Using Strength of Coke Matrix and Fluidity as Indices
This method is a blending theory in which the strength of coke is predicted using two indices, i.e., the mean maximum reflectance of vitrinite (mean value of Ro) and Gieseler maximum fluidity (MF), as coal property parameters. Currently, the blending method is commonly employed.
(ii) Method for Predicting Strength of Coke Using NMR
This method is a method for predicting the strength of coke using an index indicating the amount of coal plastic component in coal measured by NMR (Nuclear Magnetic Resonance) and an index indicating the viscosity of the coal plastic component in coal (for example, see Patent Literature 1).
(iii) Method for Predicting Strength of Coke Using Blend Effect Coefficient as Index
In common coke strength prediction expressions used in items (i), (ii), and so forth, the strength of coke produced by the carbonization of a coal blend in which a plurality of coal brands are blended is predicted by the weighted average of physical properties of coals blended. However, it is known that additivity does not hold between the strength of coke obtained from a single coal brand and the strength of coke obtained from a plurality of coal brands, in some cases. The reason the additivity does not hold is presumably due to the interaction between coal particles. In the coke strength prediction expressions in items (i) and (ii), the effect of increasing or decreasing the strength by the interaction, i.e., the blend effect, is often not considered. In contrast, the following is known: With respect to a method for predicting the blend effect, the coke properties of coke obtained from a coal blend including a plurality of coal brands are defined as coke properties of coke obtained from the set of combinations of two types of coal. The deviation of the coke properties from the weighted average of the coke properties of coke produced from a single coal brand is defined as a blend effect coefficient. A method for creating a coke strength prediction expression using the blend effect coefficient is employed (for example, see Patent Literature 2). The blend effect coefficient may be determined by actual measurement or prediction.